if you look at it from a harry potter stand point (i've been ready alot of fanfiction lol) Natsu would be the foolish gryffindor with hufflepuff tendencies, and lucy would be the ravenclaw/gryffindor/hufflepuff lol

Yes, Lucy is clearly smarter. Natsu may have pulled through more often but he operates on instinct, which doesn't make him smarter. He just knows the inner workings of his body better because of it and can push himself further than someone who stops to consider what they are doing to themselves or their situation. Lucy (while often made to display typical blond syndrome) is obviously pretty intelligent.

Natsu is good at fighting, and to be honest, not much else...except eating. His "intelligence" is merely the animal-like instincts possessed by most successful brawlers. Lucy, on the other hand, was brought up with a rich education and a well-funded personal library, so it is only natural that she would end up the "smarter" of the 2, even if she does naive things on a regular basis.

Logically Lucy's smarter. After all she's more educated than Natsu. Natsu on the other hand learned all his stuffs from a dragon. No matter how smart a dragon is, it's still a different existence from humans.

well we cant say if Lucy is more educated than Natsu. The reason why is because igneel didnt only teach Natsu dragon slayer magic but also ancient language. The truth is we don't even know how old Natsu is because back when Freed put up his rune barrier to an age restriction Natsu couldnt go through.